Power System(Transmission & Distribution)-03:

51)   The maximum tension in a section of overhead line conductor between two supports of unequal height occurs at

a. The higher support
b. The lower support
c. Midpoint of the conductors
d. None of these

52)   Safety factor is the ratio of

a. Working stress to breaking stress.
b. Breaking stress to working stress.
c. 1 / breaking stress.
d. 1 / working stress.

53)   What is the effect of temperature rise on the over head lines?

a. Increase the sag and decrease the tension
b. Decrease the sag and increase the tension
c. Both increases
d. Both decreases

54)   A transmission line has a span of 250 metres between the line supports. The conductors has a cross sectional area of 1.29 cm² and weighs 1170 kg/km and has a breaking stress of 4218 kg/cm². Calculate the sag and vertical sag with a safety factor of 5, with a wind pressure of 122 kg per square metre of the projected area.

a. 14 and 5.37
b. 16 and 8.39
c. 14 and 8.39
d. 15 and 5.37

55)   Why is stringing chart useful?

a. For finding the sag in the conductor
b. In the design of insulator string
c. In the design of tower
d. To find the distance between the towers

56)   Galloping in transmission line conductors arises due to

a. Asymmetrical layers of ice formation.
b. Vortex phenomenon in light winds.
c. Heavy weight of the line conductors.
d. Adoption of horizontal conductor configuration.

57)   What is the frequency of aeoline vibrations?

a. f_α = 2 * (V_p / d) * 1000
b. f_α = 2 * (V_p * d) * 1000
c. f_α = 2 / (V_p * d) * 1000
d. f_α = 2 / (V_p / d) * 1000

58)   What are the different types of vibrations in the vertical plane?

a. Aeoline vibrations
b. Galloping
c. Both (a) and (b)
d. None of these

59) What is the minimum clearance of HV lines from ground across the streets?

a. 3 m.
b. 6 m.
c. 5 m.
d. 8 m.

 

60)   What is the minimum horizontal clearance of a LV line from a residential building?

a. 0.6 m.
b. 0.9 m.
c. 1.2 m.
d. 1.6 m.

67)   If a 132 kV line passes over a residential building, what shall be the minimum vertical clearance from the roof of the building?

a. 3 m.
b. 4.57 m.
c. 6.38 m.
d. 9.27 m.

61)   What is the minimum clearance provided for the 132 kV line from the ground?

a. 3.2 m.
b. 6.4 m.
c. 7.5 m.
d. 10.5 m.

62)   What is the horizontal spacing between phase conductors of 132 kV line?

a. 8 m.
b. 11 m.
c. 14 m.
d. 17 m.

63)   Which type of insulator is used on 132 kV transmission lines?

a. Pin type
b. Disc type
c. Shackle type
d. Pin and shackle type

64)   Where are the strain type insulators used?

a. At dead ends
b. At any intermediate anchor tower
c. On straight runs
d. Either (a) or (b)

65)   Porcelain is produced by firing at high temperature due to mixtures of _________.

a. Kaolin
b. Feldspar
c. Quartz
d. All of these

66)   What is the dielectric strength of porcelain?

a. 55 kV/cm.
b. 60 kV/cm.
c. 75 kV/cm.
d. 80 kV/cm.

67)   Why is the wavy structure of pin insulators used?

a. Increases mechanical strength.
b. Increases puncture strength.
c. Increases flash over voltage.
d. Increases thermal strength.

68)   The number of discs in a string of insulators for 400 kV ac over head transmission line lies in the range of

a. 32 – 33
b. 22 – 23
c. 15 – 16
d. 9 – 10

69)   What is the maximum voltage level upto which the pin type insulators can be used?

a. 22 kV
b. 33 kV
c. 66 kV
d. 132 kV

70)   What is the safety factor of an insulator?

a. Puncture strength * Flash over voltage
b. Puncture strength / Flash over voltage
c. Flash over voltage / Puncture strength
d. None of these

71)   What is the desirable safety factor prescribed for the pin type of insulators?

a. 5
b. 13
c. 10
d. 2

72)   Why is the voltage rating of a multiple shell pin type insulator cannot be increased beyond a limiting value?

a. The internal voltage distribution between shells becomes unequal
b. The leakage path resistance starts reducing
c. The disruptive critical voltage for the material of the insulator is reached
d. The puncture voltage of the material of the insulator is reached

73)   Which component connects the substation to the area where power is to be distributed?

a. Distributors
b. Service mains
c. Feeders
d. All of these

 

74)   The cost of material used in a distribution circuit per kVA of the distributed power varies as

a. Square of linear dimensions of supply area.
b. Directly according to (supply area)²
c. Cube of linear dimensions of supply area
d. None of these

75)   Name the cable which connects the distributor to the consumer terminals.

a. Distributors
b. Service mains
c. Feeders
d. All of these

76)   What is the permissible limit of voltage variations allowed in the distribution systems?

a. ± 2 %
b. ± 5 %
c. ± 10 %
d. ± 6 %

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